Abstract

Coffee wilt disease (CWD), caused by Gibberella xylarioides (Fusarium
xylarioides) causes major damage to Coffea canephora grown by
smallholder farmers in the Democratic Republic of Congo and Uganda and
threatens the crop in Rwanda and Tanzania; it is also present on Coffea
arabica in Ethiopia and causes substantial losses in some areas. This
project provided an important research element that is directly linked
with a larger regional coffee rehabilitation and disease management
programme (the Regional Coffee Wilt programme, RCWP), led by the Common
Fund for Commodities (CFC). Associated funding for complementary
scientific studies was also made available under the European Union (EU)
INCO-DEV programme.

Through acquisition of a comprehensive collection of F. xylarioides
isolates from CWD affected areas in Ethiopia, Tanzania, Uganda and other
parts of Africa, application of a broad range of approaches to study
genetic and pathogenic variability and initiation of a range of
relatively simple on-farm and on-station field studies, new knowledge on
the variability and epidemiology of the CWD pathogen was gained. The
project research has revealed, for example, that very little genetic
variability exists within the CWD pathogen and suggests that two
populations, possibly clonal, are currently responsible for the disease
in these countries. Host specificity would also appear to be operating
within the pathogen, in that isolates obtained since re-emergence of the
disease on C. canephora are pathogenic either to C. arabica or to C.
canephora, but not to both coffee species, and clearly relates to the
two genetic groups. Given the occurrence of the two coffee species
within Eastern Africa, the two variants are also therefore
geographically separated. Field studies, while still in their infancy,
have helped to clarify the mechanisms of survival and transmission of
the CWD pathogen in confirming that, for example, the disease can be
spread from plant to plant through use of a machete. However, no
evidence was acquired to indicate that the pathogen survives on plants
other than coffee, or that insects are involved in disease transmission.
The various findings have major implications with regard to future
management of CWD through cultural approaches, by providing information
of relevance to the current search for durable resistance in particular.